Load control device having a reduced leakage through ground

ABSTRACT

A load control device for controlling power delivered from an AC power source to an electrical device may be configured to conduct current through earth ground and may disconnect a switching circuit to reduce an amount of current conducted through the earth ground. The load control device may comprise a controllably conductive device configured to control the power delivered from the AC power source to the electrical device so as to generate a switched-hot voltage, a switching circuit electrically coupled with a detect circuit, and a control circuit configured to render the switching circuit conductive and nonconductive. The detect circuit may generate a detect signal indicating a magnitude of the switched-hot voltage. The control circuit may be configured to monitor the detect signal and to render the switching circuit non-conductive after detecting an edge on the detect signal to reduce the total current through the earth ground.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.15/160,909, filed May 20, 2015, now U.S. Pat. No. 10,305,279, issued May28, 2019, which claims the benefit of Provisional U.S. PatentApplication No. 62/164,670, filed May 21, 2015, the entire disclosuresof which are incorporated herein by reference in their entireties.

BACKGROUND

Typical load control devices are operable to control the amount of powerdelivered to an electrical load, such as a lighting load or a motorload, from an alternating-current (AC) power source. Wall-mounted loadcontrol devices are adapted to be mounted to standard electricalwallboxes. A dimmer switch comprises a controllably conductive device(e.g., a bidirectional semiconductor switch, such as, a triac), which iscoupled in series between the power source and the load. Thecontrollably conductive device is controlled to be conductive andnon-conductive for portions of a half-cycle of the AC power source tothus control the amount of power delivered to the load (e.g., using aphase-control dimming technique). A “smart” dimmer switch (e.g., adigital dimmer switch) comprises a microprocessor (or similarcontroller) for controlling the semiconductor switch and a power supplyfor powering the microprocessor. In addition, the smart dimmer switchmay comprise a memory, a communication circuit, and a plurality oflight-emitting diodes (LEDs) that are powered by the power supply.

An electronic switch (e.g., a digital switch) comprises a controllablyconductive device (e.g., a relay or a bidirectional semiconductorswitch), a microprocessor, and a power supply. In contrast to a smartdimmer switch, the controllably conductive device of an electronicswitch is not controlled using the phase-controlled dimming technique,but is controlled to be either conductive or non-conductive during ahalf-cycle of the AC power source to thus toggle the electrical load onand off. Wall-mounted digital sensor dimmers and sensor switches mayfurther comprise occupancy detection circuits, such that the dimmers andswitches are able to operate as occupancy sensors to automatically turnon lighting loads in response to the presence of an occupant (i.e., anoccupancy condition) and automatically turn off the lighting loads inresponse to detecting the absence of an occupant (i.e., a vacancycondition).

The power supply and control circuitry of some wall-mounted digitalsensor dimmers and sensor switches may be configured to conduct currentthrough an earth ground connection. It is desirable to minimize theamount of current conducted through the earth ground connection. Forexample, standards may limit the amount of current conducted the earthground connection to approximately 500 μA or less. This may be difficultin some installations, for example, those that include occupancydetection circuits (e.g., which may be a pyroelectric infrared (PIR)detector and/or an ultrasound detector) that require relativelysubstantial current for operation.

SUMMARY

The present disclosure relates to a load control system for controllingan amount of power delivered to an electrical device (e.g., electricalload), such as a lighting load, and for controlling an amount of powerdelivered to a switching device for turning the electrical device on andoff.

A load control device for controlling power delivered from an AC powersource to an electrical device is disclosed herein. The load controldevice may comprise a first electrical connection adapted to beelectrically coupled to a hot side of the AC power source, a secondelectrical connection adapted to be electrically coupled to theelectrical device, a third electrical connection adapted to beelectrically coupled to an earth ground connection or a neutral side ofthe AC power source, and a controllably conductive device electricallycoupled between the first and second electrical connections. Thecontrollable conductive device may be configured to control the powerdelivered from the AC power source to the electrical device so as togenerate a switched-hot voltage at the second electrical connection. Theload control device may comprise a detect circuit electrically coupledbetween the second and third electrical connections and configured togenerate a detect signal indicating a magnitude of the switched-hotvoltage. The load control device may comprise a switching circuitelectrically coupled in series with the detect circuit between thesecond and third electrical connections. The load control device maycomprise a control circuit configured to render the switching circuitconductive to cause the detect circuit to begin generating the detectsignal. The control circuit may be configured to subsequently monitorthe detect signal from the detect circuit and render the switchingcircuit non-conductive after detecting an edge on the detect signal,e.g., to disconnect the detect circuit from the third electricalconnection and to reduce the total current conducted through the thirdelectrical connection.

The load control device may comprise a first hot detect circuitconfigured to generate a first hot-detect signal, a second hot detectcircuit configured to generate a second hot-detect signal, a firstswitching circuit electrically coupled between the second hot detectcircuit, and a connection that is adapted to be electrically coupled toearth ground or a neutral side of the AC power source. The load controldevice may comprise a control circuit configured to receive the firsthot-detect signal and the second hot-detect signal. The control circuitmay be configured to render the first switching circuit conductive andnon-conductive. The control circuit may be configured to determinewhether the first hot-detect signal and the second hot-detect signal arein phase. When the control circuit determines that the first hot-detectsignal and the second hot-detect signal are in phase, the controlcircuit may be configured to render the first switching circuitnon-conductive. When the control circuit determines that the firsthot-detect signal and the second hot-detect signal are out of phase, thecontrol circuit may be configured to render the first switching circuitconductive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example load control device.

FIG. 2 is a flowchart of an example control procedure.

FIG. 3 is a block diagram of another example load control device.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an example load control device 100 (e.g., aswitching module). The load control device 100 is adapted to beelectrically coupled in series between an alternating-current (AC) powersource 102 and an electrical device, e.g., an electrical load (such as alighting load) and/or a load regulation device for an electrical load(such as, an LED driver 104 for an LED light source 106). The loadcontrol device 100 may comprise a hot terminal H adapted to be coupledto the hot side of an AC power source 102 for receiving a hot voltageV_(H), and a switched-hot terminal SH adapted to be coupled to the LEDdriver 104. The load control device 100 may also comprise an earthground terminal EGND that may be coupled to an earth ground connectionin the electrical wallbox in which the load control device 100 ismounted. The load control device 100 may alternatively or additionallycomprise a neutral connection (not shown) adapted to be coupled to aneutral side of the AC power source 102.

The load control device 100 may be configured to control the powerdelivered from an AC power source to an electrical device. For exampleas shown in FIG. 1, the load control device 100 may be configured tocontrol the power delivered to the LED driver 104 and the LED lightsource 106, e.g., to turn the LED light source 106 on and off. The LEDdriver 104 may be configured to control the amount of power delivered tothe LED light source 106, and thus the intensity of the LED light source106. Examples of LED drivers are described in greater detail incommonly-assigned U.S. Pat. No. 8,492,987, issued Jul. 23, 2013,entitled LOAD CONTROL DEVICE FOR A LIGHT-EMITTING DIODE LIGHT SOURCE,and U.S. Patent Application Publication No. 2014/0009084, published Jan.9, 2014, entitled FORWARD CONVERTER HAVING A PRIMARY-SIDE CURRENT SENSECIRCUIT, the entire disclosures of which are hereby incorporated byreference. Alternatively or additionally, the electrical device mayinclude a lighting load (e.g., an incandescent or halogen lamp) and/oran electronic ballast for driving a fluorescent lamp.

The load control device 100 may comprise a controllably conductivedevice, e.g., a switching circuit, such as a relay 110, electricallycoupled in series between the hot terminal H and the switched hotterminal SH for controlling the power delivered from thealternating-current (AC) power source 102 to the LED driver 104 and theLED light source 106. The controllably conductive device may comprise abidirectional semiconductor switch, such as, for example, a triac, oneor more silicon-controlled rectifiers (SCRs), a field-effect transistor(FET) in a rectifier bridge, two FETs in anti-series connection, one ormore insulated-gate bipolar junction transistors (IGBTs), or anysuitable semiconductor switching circuit.

The load control device 100 may comprise a control circuit 112 coupledto the relay 110 for rendering the relay 110 conductive andnon-conductive to control the power delivered to the LED driver 104 andthe LED light source 106 (e.g., to turn the LED light source on andoff). For example, the control circuit 112 may be configured to generatea drive signal V_(DR) for controlling the relay 110 to be conductive andnon-conductive to generate a switched-hot voltage V_(SH) at the switchedhot terminal SH. If the relay 110 is a non-latching relay having asingle SET coil, the control circuit 112 may be configured to generate adrive signal V_(DR). The drive signal V_(DR) may be driven high (e.g.,actively driven high) to render the relay 110 conductive or driven lowto render the relay 110 non-conductive. If the relay 110 is a latchingrelay having SET and RESET coils, the control circuit 112 may generatetwo drive signals for the SET and RESET coils to render the relay 110conductive and non-conductive, respectively. If the load control device100 comprises a bidirectional semiconductor switch (e.g., thebidirectional semiconductor switch may replace the relay 110), thecontrol circuit 112 may be configured to control the bidirectionalsemiconductor switch to adjust the amount of power delivered to the LEDdriver 104 and the LED light source 106 (e.g., to adjust the intensityof the LED light source).

The control circuit 112 may comprise any suitable controller orprocessing device, such as, for example, a microprocessor, aprogrammable logic device (PLD), a microcontroller, an applicationspecific integrated circuit (ASIC), or a field-programmable gate array(FPGA). The control circuit 112 may also be coupled to a memory (notshown) for storing operational characteristics of the load controldevice 100. The memory may be implemented as an external integratedcircuit (IC) or as an internal circuit of the control circuit 112.

The load control device 100 may comprise a user interface 114 having,for example, one or more buttons (e.g., actuators) for receiving userinputs and one or more visual indicators for providing user feedback.The control circuit 112 may be configured to render the relay 110conductive and non-conductive to turn the LED light source 106 on andoff in response to actuations of the buttons of the user interface. Thecontrol circuit 112 may be configured to illuminate the visualindicators of the user interface 114 to provide, for example, a visualrepresentation of the status of the LED driver 104 and/or the LED lightsource 106 (e.g., whether the LED light source is on or off).

The load control device 100 may further comprise a sensor circuit, e.g.,an occupancy detection circuit 115 operable to detect an occupancy orvacancy condition in the vicinity of the load control device. Theoccupancy detection circuit 115 may comprise a detector (e.g., apyroelectric infrared (PIR) detector, an ultrasonic detector, and/or amicrowave detector) for detecting an occupancy or vacancy condition inthe space. For example, a PIR detector may be operable to receiveinfrared energy from an occupant in the space around the load controldevice 100 through a lens (not shown) to thus sense the occupancycondition in the space. The control circuit 112 may be configured todetermine a vacancy condition in the space around the load controldevice 100 after a timeout period expires since the last occupancycondition was detected. The control circuit 112 may be configured toturn the LED light source 106 on and off and to adjust the intensity ofthe LED light source 106 in response to the occupancy detection circuit115 detecting occupancy and/or vacancy conditions.

The load control device 100 may also comprise a communication circuit116, e.g., a wireless communication circuit for transmitting and/orreceiving wireless signals. For example, the communication circuit 116may comprise a radio-frequency (RF) transceiver, an RF receiver, an RFtransmitter, an infrared (IR) receiver, or other suitable wirelesscommunication circuit. The load control device 100 may be configured toreceive the wireless signals from input devices, such as, for example, abattery-powered remote control device and/or a wireless occupancysensor. The control circuit 112 may be configured to control the LEDlight source 106 in response to the wireless signals received via thecommunication circuit 116. Examples of remote wireless occupancy andvacancy sensors are described in greater detail in commonly-assignedU.S. Pat. No. 7,940,167, issued May 10, 2011, entitled BATTERY-POWEREDOCCUPANCY SENSOR; U.S. Pat. No. 8,009,042, issued Aug. 30, 2011,entitled RADIO-FREQUENCY LIGHTING CONTROL SYSTEM WITH OCCUPANCY SENSING;and U.S. Pat. No. 8,199,010, issued Jun. 12, 2012, entitled METHOD ANDAPPARATUS FOR CONFIGURING A WIRELESS SENSOR, the entire disclosures ofwhich are hereby incorporated by reference. Alternatively oradditionally, the communication circuit 116 may comprise a wiredcommunication circuit operable to transmit and receive digital messagesover a wired communication link, such as, for example, a serialcommunication link, an Ethernet communication link, a power-line carriercommunication link, or other suitable digital communication link.

The load control device 100 may also be responsive to other types ofinput devices, such as, for example, daylight sensors, radiometers,cloudy-day sensors, shadow sensors, window sensors, temperature sensors,humidity sensors, pressure sensors, smoke detectors, carbon monoxidedetectors, air-quality sensors, motion sensors, security sensors,proximity sensors, fixture sensors, partition sensors, keypads, kineticor solar-powered remote controls, key fobs, cell phones, smart phones,tablets, personal digital assistants, personal computers, laptops,timeclocks, audio-visual controls, safety devices (e.g., fireprotection, water protection, and/or medical emergency devices), powermonitoring devices (e.g., power meters, energy meters, utilitysubmeters, and/or utility rate meters), residential, commercial, and/orindustrial controllers, interface devices with other control systems(e.g., security systems and emergency alert systems), or any combinationof these input devices.

The load control device 100 may further comprise a power supply 118 forgenerating a direct-current (DC) supply voltage V_(CC) for powering thecontrol circuit 112, the sensor circuit 115, the wireless communicationcircuit 116, and other low-voltage circuitry of the load control device100. The power supply 118 may be electrically coupled between the hotterminal H and the earth ground terminal EGND. The power supply 118 mayalternatively be electrically coupled between the hot terminal H and aneutral terminal (e.g., rather than between the hot terminal H and theearth ground terminal EGND).

The load control device 100 may further comprise a hot detect circuit120 and/or a switched-hot detect circuit 122. The hot detect circuit 120may be coupled between the hot terminal H and the earth ground terminalEGND, and may be configured to generate a hot detect signal V_(D-H) thatindicates the magnitude of the hot voltage V_(H). The switched-hotdetect circuit 122 may be coupled between the switched-hot terminal SHand the earth ground terminal EGND, and may be configured to generate aswitched-hot detect signal V_(D-SH) that indicates the magnitude of theswitched-hot voltage V_(SH). The hot detect circuit 120 and theswitched-hot detect circuit 122 may comprise, for example, a zero-crossdetect circuit. For example, the hot detect circuit 120 may beconfigured to drive the hot detect signal V_(D-H) high towards thesupply voltage V_(CC) when the magnitude of the hot voltage V_(H) dropsbelow a hot-detect threshold (e.g., approximately 30 volts), and theswitched-hot detect circuit 122 may be configured to drive theswitched-hot detect signal V_(D-SH) high towards the supply voltageV_(CC) when the magnitude of the switched-hot voltage V_(SH) drops belowa switched-hot-detect threshold (e.g., approximately 30 volts). The hotdetect circuit 120 and the switched-hot detect circuit 122 may each beconfigured to conduct an operating current I_(OP) (e.g., approximately20 μA) through the earth ground terminal EGND in order to generate thehot detect signal V_(D-H) and the switched-hot detect signal V_(D-SH),respectively.

The control circuit 112 may be configured to receive the hot detectsignal V_(D-H) and the switched-hot detect signal V_(D-SH). The controlcircuit 112 may be configured to determine the times of thezero-crossings of the hot voltage V_(H) in response to the hot detectsignal V_(D-H) to determine when to open and close the relay 110. Thecontrol circuit 112 may be configured to measure a half-cycle timeperiod T_(HC) between consecutive zero-crossings and to store thehalf-cycle time period T_(HC) in memory. The control circuit 112 may beconfigured to determine if and/or when the relay 110 successfully openedand/or closed in response to the switched-hot detect signal V_(D-SH).

The load control device 100 may further comprise a first switchingcircuit 124 electrically coupled in series with the switched-hot detectcircuit 122. The first switching circuit 124 may be renderednon-conductive to reduce a total leakage current conducted through theearth ground (e.g., I_(L)). The control circuit 112 may be configured togenerate a first control signal V_(CON1) for controlling the firstswitching circuit 124 to open and close. The control circuit 112 may beconfigured to render the first switching circuit 124 conductive, monitorthe switched-hot detect signal V_(D-SH) when the first switching circuit124 is conductive, and render the first switching circuit 124non-conductive after detecting an edge on the switched-hot detect signalV_(D-SH). The control circuit 112 may be configured to render the firstswitching circuit 124 conductive to enable the switched-hot detectcircuit 122 to generate the switched-hot detect signal V_(D-SH) and toallow the control circuit 112 to be responsive to the switched-hotdetect signal V_(D-SH). The control circuit 112 may be configured toopen the first switching circuit 124 when the control circuit 112 doesnot need to be responsive to the switched-hot detect signal V_(D-SH),such that the switched-hot detect circuit 122 does not conduct theoperating current I_(OP) through the earth ground terminal EGND (e.g.,to reduce the total leakage current I_(L) conducted through the earthground terminal EGND).

The control circuit 112 may be configured to determine if the relay 110is open or closed by rendering the first switching circuit 124conductive and monitoring the switched-hot detect signal V_(D-SH)generated by the switched-hot detect circuit 122. For example, thecontrol circuit 112 may be configured to determine if the relay 110 isopen or closed at startup by rendering the first switching circuit 124conductive. The control circuit 112 may be configured to determine thatthe relay 110 is open if the switched-hot detect circuit 122 is notgenerating the switched-hot detect signal V_(D-SH) and to determine thatthe relay 110 is closed if the switched-hot detect circuit 122 isgenerating the switched-hot detect signal V_(D-SH).

The load control device 100 may also comprise a second switching circuit126 electrically coupled in series with the hot detect circuit 120 fordisconnecting the hot detect circuit to further reduce the total currentconducted through the earth ground terminal EGND (e.g., the totalleakage current I_(L)). The control circuit 112 may be configured togenerate a second control signal V_(CON2) for controlling the secondswitching circuit 126 to open and close the second switching circuit126. In some instances, the second switching circuit 126 may be omitted.

The first switching circuit 124 and/or the second switching circuit 126may comprise a bidirectional semiconductor switch, such as, for example,a triac, one or more silicon-controlled rectifiers (SCRs), afield-effect transistor (FET) in a rectifier bridge, two FETs inanti-series connection, one or more insulated-gate bipolar junctiontransistors (IGBTs), a half wave rectifier diode in anti-series with asingle FET, or any suitable semiconductor switching circuit.

When closing the relay 110, the control circuit 112 may attempt tocontrol the relay such that the contacts of the relay are closed asclose as possible to a zero-crossing of the hot voltage V_(H), e.g., tominimize arcing across the contacts of the relay. There may be a delaybetween the time at which the control circuit 112 controls the drivesignal V_(DR) to close the relay 110 and the time at which the contactsof the relay finally close. This delay may be dependent upon an internaldelay of the relay 110 and/or a hardware delay of the load controldevice 100. In addition, the relay 110 may be characterized by a bouncetime period while the contacts of the relay are bouncing, e.g., betweenthe time at which the contacts first make contact with each other andthe time at which the contacts stop bouncing. The control circuit 112may be configured to control the drive signal V_(DR) to close the relay110 at a time that is within a relay close adjustment time periodT_(CL-ADJ) before an upcoming zero-crossing (e.g., at the beginning ofthe relay close adjustment time period T_(CL-ADJ)), such that the relay110 typically finishes bouncing prior to the upcoming zero-crossing.

The length of the relay close actuation adjustment time periodT_(CL-ADJ) may change with time, e.g., as the relay 110 and/or the otherelectrical components of the load control device 100 age. The controlcircuit 112 may be configured to measure the delay between the time atwhich the control circuit 112 controls the drive signal V_(DR) to closethe relay 110 and the time at which the contacts of the relay 110finally close in response to the switched-hot detect signal V_(D-SH)generated by the switched-hot detect circuit 122. The control circuit112 may be configured to monitor the switched-hot detect signal V_(D-SH)to determine if the relay 110 is closed where desired, e.g., totypically finish bouncing before a zero-crossing of the hot voltageV_(H). The control circuit 112 may be configured to adjust the relayclose adjustment time period T_(CL-ADJ) in response to determining thatthe relay 110 did not close where desired, e.g., to typically finishbouncing before a zero-crossing of the hot voltage V_(H). The controlcircuit 112 may be configured to render the first switching circuit 124conductive before attempting to close the relay 110, such that thecontrol circuit is able to receive the switched-hot detect signalV_(D-SH) near the zero-crossing at which the control circuit is tryingto close the relay 110. The control circuit 112 may be configured torender the first switching circuit 124 non-conductive after detecting anedge of the switched-hot detect signal V_(D-SH) (e.g., after thezero-crossing at which the control circuit is trying to close the relay110). The control circuit 112 may be configured to monitor theswitched-hot detect signal V_(D-SH) (e.g., in order to adjust the relayclose adjustment time period T_(CL-ADJ)) until the first switchingcircuit 124 is non-conductive.

When opening the relay 110, the control circuit 112 may be configured tocontrol the drive signal V_(DR) to open the relay 110 at a time that isa relay open adjustment time period T_(OP-ADJ) before an upcomingzero-crossing. The relay open adjustment time period T_(OP-ADJ) may bedifferent from the relay actuation adjustment time period T_(CL-ADJ).When opening the relay 110, the control circuit 112 may be configured torender the first switching circuit 124 conductive before attempting toopen the relay, and to render the first switching circuit 124non-conductive after detecting an edge of the switched-hot detect signalV_(D-SH).

A load control device configured to adjust a relay close adjustment timeused to close a relay and a relay open adjustment time used to open arelay is described in greater detail in commonly-assigned U.S. PatentApplication Publication No. 2015/0098164, published Apr. 9, 2015,entitled CONTROLLING A CONTROLLABLY CONDUCTIVE DEVICE BASED ONZERO-CROSSING DETECTION, the entire disclosure of which is herebyincorporated by reference.

The control circuit 112 may be configured to determine a fault condition(e.g., if the relay 110 did not successfully open or close) in responseto the switched-hot detect signal V_(D-SH). The control circuit 112 maybe configured to render the first switching circuit 124 conductivebefore attempting to open the relay, and to render the first switchingcircuit 124 non-conductive after detecting that the relay openedproperly or is stuck closed. For example, the control circuit 112 may beconfigured to determine if the relay opened successfully by monitoringthe switched-hot detect signal V_(D-SH) for a detect time period (e.g.,approximately 15 milliseconds) after controlling drive signal V_(DR) torender the relay non-conductive. If the control circuit 112 detects thatthe switched-hot voltage V_(SH) is not present (e.g., the magnitude ofthe switched-hot voltage is approximately zero volts) at theswitched-hot terminal SH at the end of the detect time period, thecontrol circuit 112 may conclude that the relay opened properly andcontinue normal operation. However, if the switched-hot voltage ispresent, the control circuit 112 may conclude that the relay 110 isstuck closed and operate in a fault mode. If the control circuit 112determines that the relay is stuck closed, the control circuit 112 mayattempt to fix the stuck relay by periodically attempting to closeand/or open the relay for a predetermined number of times. A loadcontrol device configured to detect a stuck relay is described ingreater detail in commonly-assigned U.S. patent application Ser. No.15/087,838, filed Mar. 31, 2016, entitled LOAD CONTROL DEVICE HAVINGSTUCK RELAY DETECTION, the entire disclosure of which is herebyincorporated by reference.

If the relay 100 is a latching relay, the control circuit 112 may or maynot know the state of the relay (e.g., the state of being open orclosed) in the event of a power failure (e.g., after losing and onceagain receiving power). The control circuit 112 may be configured tomonitor the hot detect signal V_(D-H) and the switched-hot detect signalV_(D-SH) to determine the state of the relay immediately after beingpowered up. For example, if the control circuit 112 is receiving the hotdetect signal V_(D-H), but not the switched-hot detect signal V_(D-SH),the control circuit may conclude that the relay 110 is open. If thecontrol circuit 112 is receiving both of the hot detect signal V_(D-H)and the switched-hot detect signal V_(D-SH), the control circuit mayconclude that the relay 110 is closed.

The load control device 100 may be configured to operate correctly evenif the hot and switched hot terminals H, SH (as shown in FIG. 1) arewired up backwards (e.g., if the hot terminal H is coupled to the LEDdriver 104 and the switched-hot terminal SH is coupled to the hot sideof the AC power source 102). To enable this functionality, the powersupply 118 may be coupled to the hot terminal H and the switched-hotterminal SH via respective diodes, such that the power supply 118 isable to charge if the AC power source 102 is coupled to either of thehot and switched-hot terminals H, SH. After being powered up, thecontrol circuit 112 may be configured to maintain the relay 110non-conductive and then render the second switching circuit 126conductive to determine if the hot detect circuit 120 is generating thehot detect signal V_(D-H). If the hot detect circuit 120 is generatingthe hot detect signal V_(D-H), the control circuit 112 may conclude thatthe hot terminal H is coupled to the hot side of the AC power source 102and may control the relay 110 and the first switching circuit 124 duringnormal operation as described above (e.g., to render the first switchingcircuit conductive before attempting to close or open the relay, andnon-conductive after detecting an edge of switched-hot detect signalV_(D-SH)). In addition and for example, the control circuit 112 mayrender the second switching circuit 126 conductive at all times duringnormal operation, such that the hot detect circuit 120 always generatesthe hot detect signal V_(D-H).

If the control circuit 112 determines that the hot detect circuit 120 isnot generating the hot detect signal V_(D-H), the control circuit 112may be configured to render the second switching circuit 126non-conductive and then render the first switching circuit 124conductive to determine if the switched-hot detect circuit 122 isgenerating the switched-hot detect signal V_(D-SH). If the switched-hotdetect circuit 122 is generating the switched-hot detect signalV_(D-SH), the control circuit 112 may assume that the hot and switchedhot terminals H, SH are wired up backwards, e.g., that the switched-hotterminal SH is coupled to the hot side of the AC power source 102. Thus,during normal operation, the control circuit 112 may render the secondswitching circuit 126 conductive before attempting to close or open therelay, and non-conductive after detecting an edge of hot detect signalV_(D-H). In addition and for example, the control circuit 112 may renderthe first switching circuit 124 conductive at all times during normaloperation, such that the switched-hot detect circuit 122 alwaysgenerates the switched-hot detect signal V_(D-SH).

The load control device 100 be configured to control the power to othertypes of electrical loads, such as, for example, lighting loads (e.g.,such as incandescent lamps, halogen lamps, electronic low-voltagelighting loads, and magnetic low-voltage lighting loads); dimmingballasts for driving gas-discharge lamps; table or floor lamps; screw-inluminaires including dimmer circuits and incandescent or halogen lamps;screw-in luminaires including ballasts and compact fluorescent lamps;screw-in luminaires including LED drivers and LED light sources; motorloads, such as ceiling fans and exhaust fans; motorized windowtreatments; projection screens; motorized interior or exterior shutters;heating and/or cooling systems; heating, ventilation, andair-conditioning (HVAC) systems; air conditioners; compressors; electricbaseboard heater controllers; controllable dampers; variable air volumecontrollers; fresh air intake controllers; ventilation controllers;hydraulic valves for use in radiators and radiant heating system;humidity control units; humidifiers; dehumidifiers; water heaters;boiler controllers; pool pumps; refrigerators; freezers; appliances;televisions; computer monitors; printers; copiers; fax machines; videocameras; audio systems; amplifiers; speakers; overhead projectors;visual presenters; smart boards; coffee makers; toasters; elevators;power supplies; generators; electric chargers; electric vehiclechargers; medical devices, alternative energy controllers, and/or anycombination of these electrical loads.

FIG. 2 is a flowchart of an example command procedure 200 for openingand closing a relay. The command procedure 200 may be executed by acontrol circuit of a load control device (e.g., the control circuit 112of the load control device 100) in response to receiving a command at210 (e.g., via the user interface 114 and/or the communication circuit116). At 212, the control circuit may be configured to determine anappropriate value for the relay close adjustment time period T_(CL-ADJ)or the relay open adjustment time period T_(OP-ADJ). The relay closeadjustment time period T_(CL-ADJ) may be a time period between when therelay drive voltage is adjusted and a subsequent zero-crossing at whichthe control circuit is attempting to cause the controllably conductivedevice to become conductive (e.g., a time interval between when therelay closure is initiated and a subsequent zero-crossing). The relayopen adjustment time period T_(OP-ADJ) may be a time period between whenthe relay drive voltage is adjusted and a subsequent zero-crossing atwhich the control circuit is attempting to cause the controllablyconductive device non-conductive (e.g., a time interval between when therelay opening is initiated and a subsequent zero-crossing).

The control circuit may be configured to control the first controlsignal V_(CON1) to render the first switching circuit 124 conductive at214, such that the control circuit is able to receive the switched-hotdetect signal V_(D-SH). After detecting a zero-crossing at 216 (e.g., inresponse to the hot detect signal V_(D-H)), the control circuit may waitat 217 for a wait time period T_(WAIT), which may be equal to orrelatively equal to, for example, the relay close adjustment time periodT_(CL-ADJ) minus the half-cycle time period T_(HC) or the relay openadjustment time period T_(OP-ADJ) minus the half-cycle time periodT_(HC). The half-cycle time period T_(HC) may be a time period betweenconsecutive zero-crossings (e.g., zero-crossings of V_(H1) and/orV_(H2)).

At the end of the wait time period T_(WAIT), the control circuit may beconfigured to control the drive signal V_(DR) to open or close therelay. If the received command is determined to be an on command at 218,the control circuit may control the drive signal V_(DR) to close therelay at 220. If the relay is a latching relay, the control circuit maygenerate a first drive signal to drive the SET coil high at 220 andgenerate a second drive signal to drive the RESET coil high at 224.After controlling the drive signal V_(DR), the control circuit maydetermine (e.g., wait and determine) whether an edge on the switched-hotdetect signal V_(D-SH) appears at 226. When the control circuit receivesan edge on the switched-hot detect signal V_(D-SH) at 226, the controlcircuit may determine if the relay close adjustment time periodT_(CL-ADJ) or the relay open adjustment time period T_(OP-ADJ) needs tobe adjusted to move the opening and/or closing of the relay closer tothe zero-crossing at 228.

If the control circuit determines the relay close adjustment time periodT_(CL-ADJ) or the relay open adjustment time period T_(OP-ADJ) needs tobe adjusted to move the opening and/or closing of the relay closer tothe zero-crossing, the control circuit may, at 230, adjust the relayclose adjustment time period T_(CL-ADJ) or the relay open adjustmenttime period T_(OP-ADJ) appropriately such that the control circuit mayuse the adjusted close adjustment time period T_(CL-ADJ) or adjusted therelay open adjustment time period T_(OP-ADJ) when the control circuitsubsequently attempts to close or open the relay, respectively, and theprocedure 200 may go to 232. At 232, the control circuit may control thefirst control signal V_(CON1) to render a switching circuit (e.g., thefirst switching circuit 124 in FIG. 1) non-conductive, before thecommand procedure 200 exits. If the control circuit determines, at 228,that the relay close adjustment time period T_(CL-ADJ) or the relay openadjustment time period T_(OP-ADJ) does not need to be adjusted, thecontrol circuit may control the first control signal V_(CON1) to rendera switching circuit (e.g., the first switching circuit 124 in FIG. 1)non-conductive at 232, before the command procedure 200 exits.

If the received command is determined to be an off command at 222, thecontrol circuit may control the drive signal V_(DR) to open the relay at224. If the control circuit determines that the command is not an oncommand at 218 or an off command at 222, the control circuit may controlthe first control signal V_(CON1) to render the first switching circuit124 non-conductive at 232, before the command procedure 200 exits.

FIG. 3 is a block diagram of an example load control device 300 (e.g., adual-circuit switching module). The load control device 300 may comprisea first hot terminal H1 adapted to be coupled to the hot side of a firstAC power source 302A (e.g., a 120 VAC source) for receiving a first hotvoltage V_(H1), and a second hot terminal H2 adapted to be coupled tothe hot side of a second AC power source 302B (e.g., a 277 VAC source)for receiving a second hot voltage V_(H2). Alternatively, the first andsecond hot terminal H1, H2 may be adapted to be coupled to the hot sideof a single AC power source. The load control device 300 may comprise anearth ground terminal EGND that may be coupled to an earth groundconnection (e.g., the earth ground connection in an electrical wallboxin which the load control device 300 is mounted). The load controldevice 300 may comprise a neutral connection (not shown) adapted to becoupled to the neutral side of the AC power source 302A and/or 302B. Theload control device 300 may further comprise first and secondswitched-hot terminals SH1, SH2 adapted to be coupled to respectiveelectrical devices (e.g., electrical loads 304A, 304B, and/or loadregulation devices).

The load control device 300 may be configured to control the powerdelivered to the electrical loads 304A, 304B. The load control device300 may comprise a first controllably conductive device (e.g., a firstrelay 310A) electrically coupled in series between the first hotterminal H1 and the first switched hot terminal SH1 for controlling thepower delivered to the first electrical load 304A. The load controldevice 300 may comprise a second controllably conductive device (e.g., asecond relay 310B) electrically coupled in series between the second hotterminal H2 and the second switched hot terminal SH2 for controlling thepower delivered to the second electrical load 304B.

The load control device 300 may comprise a control circuit 312 coupledto the first and second relays 310A, 310B for rendering (e.g.,independently) the relays 310A, 310B conductive and non-conductive tocontrol the power delivered to the first and second electrical devices(e.g., loads) 304A, 304B, respectively. For example, the control circuit312 may be configured to generate a first drive signal V_(DR1) forcontrolling the first relay 310A to be conductive and non-conductive togenerate a first switched-hot voltage V_(SH1) at the first switched hotterminal SH1. The control circuit 312 may be configured to generate asecond drive signal V_(DR2) for controlling the second relay 310B to beconductive and non-conductive to generate a second switched-hot voltageV_(SH1) at the second switched hot terminal SH2. The control circuit 312may comprise any suitable controller or processing device, such as, forexample, a microprocessor, a programmable logic device (PLD), amicrocontroller, an application specific integrated circuit (ASIC), or afield-programmable gate array (FPGA). The control circuit 312 may alsobe coupled to a memory (not shown) for storing operationalcharacteristics of the load control device 300. The memory may beimplemented as an external integrated circuit (IC) or as an internalcircuit of the control circuit 312.

While not shown in FIG. 3, the load control device 300 may also comprisea user interface, an occupancy detection circuit, and/or a communicationcircuit that are similar to the user interface 114, the occupancydetection circuit 115, and the communication circuit 116, respectively,of the load control device 100 shown in FIG. 1. In addition, the loadcontrol device 300 may further comprise a power supply (not shown)configured to generate a direct-current (DC) supply voltage V_(CC) forpowering the circuitry of the load control device 300. The power supplymay, for example, be electrically coupled between the first hot terminalH1 and the earth ground terminal EGND.

The load control device 300 may comprise a first hot detect circuit 320Aelectrically coupled between the first hot terminal H1 and the earthground terminal EGND, and a second hot detect circuit 320B electricallycoupled between the second hot terminal H2 and the earth ground terminalEGND. The first and second hot detect circuit 320A, 320B may beconfigured to generate respective first and second hot detect signalsV_(D-H1), V_(D-H2) that indicate the magnitude of the voltages at thefirst and second hot terminals H1, H2, respectively. The load controldevice 300 may further comprise a first switching circuit 324A. Thefirst switching circuit 324A may be electrically coupled in series withone of the hot detect circuits 320A and 320B. For example, the firstswitching circuit 324A may be electrically coupled in series with thesecond hot detect circuit 320B, as shown in FIG. 3. While not shown inFIG. 3, the load control device 300 may also comprise a switchingcircuit electrically coupled in series with the first hot detect circuit320A.

The control circuit 312 may be configured to generate a first controlsignal V_(CON1) for controlling the first switching circuit 324A, asecond control signal V_(CON2) for controlling the second switchingcircuit 324B, and a third control signal V_(CON3) for controlling thethird switching circuit 324C. The control circuit 312 may be configuredto close the first switching circuit 324A to enable the second hotdetect circuit 320B to generate the second hot detect signal V_(D-H2).The control circuit 312 may be configured to close the second switchingcircuit 324B to enable the first switched-hot detect circuit 322A togenerate the first switched-hot detect signal V_(D-SH1). The controlcircuit 312 may be configured to close the third switching circuit 324Cto enable the second switched-hot detect circuit 322B to generate thesecond switched-hot detect signal V_(D-SH2).

The load control device 300 may further comprise a first switched-hotdetect circuit 322A electrically coupled between the first switched-hotterminal SH1 and the earth ground terminal EGND, and a secondswitched-hot detect circuit 322B electrically coupled between the secondswitched-hot terminal SH2 and the earth ground terminal EGND. The firstand second switched-hot detect circuit 322A, 322B may be configured togenerate respective first and second switched-hot detect signalsV_(D-SH1), V_(D-SH2) that indicate the magnitude of the voltages at thefirst and second switched-hot terminals SH1, SH2, respectively. The hotdetect circuits 320A, 320B and the switched-hot detect circuits 322A,322B may comprise, for example, a zero-cross detect circuit, and may besimilar to the hot detect circuit 120 and the switched-hot detectcircuit 122 described above with reference to FIG. 1. The load controldevice 300 may further comprise a second switching circuit 324B and athird switching circuit 324C. For example, the second switching circuit324B may be electrically coupled in series with the first switched-hotdetect circuit 322A, and a third switching circuit 324C may beelectrically coupled in series with the second switched-hot detectcircuit 322B.

The control circuit 312 may be configured to receive the first andsecond hot detect signals V_(D-H1), V_(D-H2) and the first and secondswitched-hot detect signals V_(D-SH1), V_(D-SH2). The control circuit312 may be configured to determine times of zero-crossings of the firstand second hot voltages V_(H1), V_(H2) in response to the respectivefirst and second hot detect signal V_(D-H1), V_(D-H2) to determine whento open and close the relay of the first and second relays 310A, 310B,respectively. The control circuit 312 may be configured to determine ifand/or when the relays 310A, 310B successfully opened and/or closed inresponse to the switched-hot detect signals V_(D-SH1), V_(D-SH2). Thecontrol circuit 312 may render the second switching circuit 324Bnon-conductive, e.g., when the control circuit 312 determines that therelay 310A successfully opened and/or closed in response to theswitched-hot detect signal V_(D-SH1). The control circuit 312 may renderthe third switching circuit 324C non-conductive, e.g., when the controlcircuit 312 determines that the relay 310B successfully opened and/orclosed in response to the switched-hot detect signal V_(D-SH2). When thecontrol circuit 312 renders one or more of the second switching circuit324B or the third switching circuit 324C non-conductive, the currentconducted through the earth ground terminal EGND (e.g., total leakagecurrent I_(L)) may be reduced.

The control circuit 312 may reduce the leakage current conducted throughthe earth ground terminal EGND (e.g., total leakage current I_(L)), forexample, by opening one or more of the first, second, and thirdswitching circuits 324A, 324B, 324C. The control circuit 312 may openone or more of the first, second, and third switching circuits 324A,324B, 324C when the control circuit 312 does not need to be responsiveto the respective detect signals V_(D-H2), V_(D-SH1), V_(D-SH2). Forexample, the control circuit 312 may be configured to open the firstswitching circuit 324A when the control circuit 312 does not need thesecond hot detect circuit 320B to generate the second hot detect signalV_(D-H2). When the first switching circuit 324A is open, a path forpotential leakage current conducted through the earth ground terminalEGND is removed. For example, the control circuit 312 may not need thesecond hot detect circuit 320B to generate the second hot detect signalV_(D-H2) when the first hot-detect signal V_(D-H1) and the secondhot-detect signal V_(D-H2) are in phase, as described in more detailherein The control circuit 312 may be configured to determine whetherthe relays 310A and/or 310B are open or closed at the startup by closingone or more of the first, second, and third switching circuits 324A,324B, 324C.

The control circuit 312 may reduce the leakage current conducted throughthe earth ground terminal EGND (e.g., total leakage current I_(L)) byopening the second switching circuit 324B and/or the third switchingcircuit 324C. For example, the control circuit 312 may be configured toopen the second switching circuit 324B when the control circuit 312 doesnot need the first switched-hot detect circuit 322A to generate thefirst switched-hot detect signal V_(D-SH1). The control circuit 312 maybe configured to open the third switching circuit 324C when the secondswitched-hot detect circuit 322B does not need to generate the secondswitched-hot detect signal V_(D-SH2). For example, the control circuit312 may not need the first switched-hot detect signal V_(D-SH1) when therelay 310A is not being adjusted (e.g., resting in the open or closedposition), and/or when the control circuit 312 determines that thetiming for delivering power from the AC power source 302A to theelectrical device 304A (e.g., T_(CL-ADJ1) and/or T_(OP-ADJ1)) does notneed to be adjusted. Similarly, the control circuit 312 may not need thesecond switched-hot detect signal V_(D-SH2) when the relay 310B is notbeing adjusted (e.g., resting in the open or closed position), and/orwhen the control circuit determines that the timing for delivering powerfrom the AC power source 302B to the electrical device 304B (e.g.,T_(CL-ADJ2) and/or T_(OP-ADJ2)) does not need to be adjusted.

The control circuit 312 may be configured to determine whether the firsthot-detect signal V_(D-H1) and the second hot-detect signal V_(D-H2) arein phase (e.g., and, for example, are the same or different magnitudes,e.g., voltages). The determination whether V_(D-H1) and V_(D-H2) are inphase may be performed at the startup. For example, the first hotterminal H1 and the second hot terminal H2 may be connected to differentAC power sources (e.g., as shown in FIG. 3), which may be in phase orout-of-phase with one another. Alternatively, the first hot terminal H1and the second hot terminal H2 may be connected to the same or differentphases of a single AC power source (e.g., a single or multi-phase ACpower source). As such, the first hot-detect signal V_(D-H1) (e.g., thefirst hot terminal H1) may be characterized by a first phase and thesecond hot-detect signal V_(D-H2) (e.g., the second hot terminal H2) maybe characterized by a second, possibly different phase. The controlcircuit 312 may be configured to determine whether the first hot-detectsignal V_(D-H1) and the second hot-detect signal V_(D-H2) are in phase,e.g., by comparing the respective first and second hot detect signalsV_(D-H1), V_(D-H2) and determining the respective zero-crossing times ofthe first and second hot voltages V_(H1), V_(H2). If the control circuit312 determines that the zero-crossing times of the first and second hotvoltages V_(H1), V_(H2) are the same, then the control circuit 312 maydetermine that the first and hot-detect signals V_(D-H1), V_(D-H2) arein phase.

When the control circuit determines that the first and second hot-detectsignals V_(D-H1), V_(D-H2) are in phase, the control circuit 312 may beconfigured to render the first switching circuit 324A non-conductive(e.g., which may reduce the current conducted through the earth groundterminal EGND (e.g., total leakage current I_(L)). For example, when thefirst hot-detect signal V_(D-H1) and the second hot-detect signalV_(D-H2) are in phase, the control circuit 312 can rely on the first hotdetect signal V_(D-H1) to determine zero-crossing events for both thefirst and second hot voltages V_(H1), V_(H2). When the control circuit312 determines that the first hot-detect signal V_(D-H1) and the secondhot-detect signal V_(D-H2) are out of phase, the control circuit 312 maybe configured to render the first switching circuit 324A conductive.Alternatively or additionally, even if the control circuit 312determines that the first hot-detect signal V_(D-H1) and the secondhot-detect signal V_(D-H2) are out of phase, the control circuit 312 maybe configured to keep the first switching circuit 324A open (e.g.,non-conductive) until the control circuit 312 receives a user input viathe user interface indicating that the relay 310B is to be closed. Uponreceiving a user input indicating that the relay 310B is to be closed,the control circuit 312 may render the first switching circuit 324Aconductive, which, for example, may allow the control circuit 312 todetermine a zero-crossing event of the hot voltage V_(H2) (e.g., and inturn, close the relay 310B as close to a zero-crossing event aspossible).

The control circuit 312 may be configured to independently open andclose the first, second, and third switching circuits 324A, 324B, 324C(e.g., at different times), or may control the open the first, second,and third switching circuits 324A, 324B, 324C in unison (e.g., at thesame time). For example, the control circuit 312 may be configured togenerate a first control signal V_(CON1) for rendering the firstswitching circuit 324A conductive and non-conductive (e.g., open andclosed), a second control signal V_(CON2) for rendering the secondswitching circuit 324B conductive and non-conductive conductive (e.g.,open and closed), and a third control signal V_(CON3) for controllingthe third switching circuit 324C conductive and nonconductive (e.g.,open and closed). Alternatively, the control circuit 312 may beconfigured to generate a single control signal for rendering two or moreof the first, second, and third switching circuits 324A, 324B, 324Cconductive and non-conductive (e.g., at the same time). The use of asingle control signal for rendering two or more of the switchingcircuits 324A, 324B, 324C conductive and/or non-conductive may, forexample, be beneficial if the control circuit includes a microprocessorthat has a limited number of ports.

When closing the relays 310A, 310B, the control circuit 312 may attemptto control the relays such that the contacts of the relays are closed asclose as possible to zero-crossings of the respective hot voltageV_(H1), V_(H2) (e.g., similar as described above with respect to FIG.1). The control circuit 312 may be configured to control the first drivesignal V_(DR1) at a time that is a first relay close adjustment timeperiod T_(CL-ADJ1) before an upcoming zero-crossing, so as to attempt toclose the first relay 310A at the upcoming zero-crossing. The controlcircuit 312 may be configured to control the second drive signal V_(DR2)at a time that is a second relay close adjustment time periodT_(CL-ADJ2) before an upcoming zero-crossing, so as to attempt to closethe second relay 310B at the upcoming zero-crossing. The control circuit312 may be configured to monitor the first and second switched-hotdetect signals V_(D-SH1), V_(D-SH2) to determine if the relays 310A,310B are closed where desired, e.g., to typically finish bouncing beforethe zero-crossing. The control circuit 112 may be configured to adjustthe relay close adjustment time periods T_(CL-ADJ1), T_(CL-ADJ2) inresponse to determining that the respective relay 310A, 310B did notclose where desired.

The control circuit 312 may be configured to render the first, second,and/or third switching circuits 324A, 324B, and/or 324C conductivebefore attempting to close the first and/or second relays 310A, 310B.When controlling the first relay 310A, the control circuit 312 may beconfigured to render the second switching circuit 324B conductive beforeattempting to close the first relay 310A, such that the control circuit312 is able to monitor the first switched-hot detect signal V_(D-SH1)near the zero-crossing at which the control circuit is trying to closethe first relay 310A. The control circuit 312 may be configured torender the second switching circuit 324B non-conductive after detectingan edge of first switched-hot detect signal V_(D-SH1) (e.g., after thezero-crossing at which the control circuit is trying to close the firstrelay 310A).

When controlling the second relay 310B and when the first hot-detectsignal V_(D-H1) and the second hot-detect signal V_(D-H2) are in phase,the control circuit 312 may be configured to render the third switchingcircuit 324C conductive before attempting to close the second relay 310B(e.g., and leave the first switching circuits 324A open), such that thecontrol circuit 312 is able to receive the second switched-hot detectsignal V_(D-SH2) near the zero-crossing at which the control circuit istrying to close the second relay 310B. Further, the control circuit 312may receive the first hot detect signal V_(D-H1) before controlling thesecond drive signal V_(DR2) (e.g., to determine zero-crossing of thesecond hot voltage V_(H2)). The control circuit 312 may be configured torender the third switching circuits 324C non-conductive after detectingan edge of second switched-hot detect signal V_(D-SH2) (e.g., after thezero-crossing at which the control circuit is trying to close the secondrelay 310B).

When controlling the second relay 310B and when the first hot-detectsignal V_(D-H1) and the second hot-detect signal V_(D-H2) are out ofphase, the control circuit 312 may be configured to render the first andthird switching circuits 324A, 324C conductive before attempting toclose the second relay 310B, such that the control circuit 312 is ableto receive the second hot detect signal V_(D-H2) before controlling thesecond drive signal V_(DR2), and to receive the second switched-hotdetect signal V_(D-SH2) near the zero-crossing at which the controlcircuit is trying to close the second relay 310B. The control circuit312 may be configured to render the third switching circuits 324Cnon-conductive after detecting an edge of second switched-hot detectsignal V_(D-SH2) (e.g., after the zero-crossing at which the controlcircuit is trying to close the second relay 310B).

When controlling the first relay 310A and the second relay 310B, andwhen the first hot-detect signal V_(D-H1) and the second hot-detectsignal V_(D-H2) are in phase, the control circuit 312 may be configuredto render the second switching circuit 324B and the third switchingcircuit 324C conductive before attempting to close the first relay 310Aand the second relay 310B. The control circuit 312 may receive the firsthot detect signal V_(D-H1) before controlling the first and second drivesignals V_(DR1), V_(DR2). The control circuit 312 may be able to monitorthe first switched-hot detect signal V_(D-SH1) near the zero-crossing atwhich the control circuit is trying to close the first relay 310A. Thecontrol circuit 312 may be configured to render the second switchingcircuit 324B non-conductive after detecting an edge of firstswitched-hot detect signal V_(D-SH1) (e.g., after the zero-crossing atwhich the control circuit is trying to close the first relay 310A). Thecontrol circuit 312 may monitor the second switched-hot detect signalV_(D-SH2) near the zero-crossing at which the control circuit is tryingto close the second relay 310B. The control circuit 312 may beconfigured to render the third switching circuits 324C non-conductiveafter detecting an edge of second switched-hot detect signal V_(D-SH2)(e.g., after the zero-crossing at which the control circuit is trying toclose the second relay 310B).

When controlling the first relay 310A and the second relay 310B, andwhen the first hot-detect signal V_(D-H1) and the second hot-detectsignal V_(D-H2) are out of phase, the control circuit 312 may beconfigured to render the first switching circuit 324A, the secondswitching circuit 324B, and the third switching circuit 324C conductivebefore attempting to close the first relay 310A and the second relay310B. The control circuit 312 may monitor the first switched-hot detectsignal V_(D-SH1) near the zero-crossing at which the control circuit istrying to close the first relay 310A. The control circuit 312 may beconfigured to render the second switching circuit 324B non-conductiveafter detecting an edge of first switched-hot detect signal V_(D-SH1)(e.g., after the zero-crossing at which the control circuit is trying toclose the first relay 310A). The control circuit 312 may monitor thesecond hot detect signal V_(D-H2) before controlling the second drivesignal V_(DR2), and to receive the second switched-hot detect signalV_(D-SH2) near the zero-crossing at which the control circuit is tryingto close the second relay 310B. The control circuit 312 may beconfigured to render the third switching circuits 324C non-conductiveafter detecting an edge of second switched-hot detect signal V_(D-SH2)(e.g., after the zero-crossing at which the control circuit is trying toclose the second relay 310B).

When opening the first and second relays 310A, 310B, the control circuit312 may be configured to control the first drive signal V_(DR1) to openthe first relay 310A at a time that is a first relay open adjustmenttime period T_(OP-ADJ1) before an upcoming zero-crossing, and to controlthe second drive signal V_(DR2) to open the second relay 310B at a timethat is a second relay open adjustment time period T_(OP-ADJ2) before anupcoming zero-crossing. When opening the first relay 310A, the controlcircuit 312 may be configured to render the second switching circuit324B conductive before attempting to open the first relay, and to renderthe second switching circuit 324B non-conductive after detecting an edgeof first switched-hot detect signal V_(D-SH1). When opening the secondrelay 310B, the control circuit 312 may be configured to render thefirst and third switching circuits 324A, 324C conductive beforeattempting to open the first relay, and to render the first and thirdswitching circuits 324A, 324C non-conductive after detecting an edge ofsecond switched-hot detect signal V_(D-SH2). Further, in one or moreembodiments, the control circuit 312 may render the first, second,and/or third switching circuits 324A, 324B, and/or 324C conductive in abefore attempting to open the first and/or second relays 310A, 310B in asimilar fashion as described herein with respect to attempting to closethe first and/or second relays 310A, 310B.

In addition, the control circuit 312 may be configured to render one ormore of the first, second, and third switching circuits 324A, 324B, 324Cconductive at startup (e.g., when power is first provided to the controlcircuit). For example, the control circuit 312 may be configured torender the first switch circuit 324A conductive for a short period oftime after startup to determine if the second hot voltage V_(H2) ispresent at the second hot terminal H2. If the second hot voltage V_(H2)is not present at the second hot terminal H2, the control circuit 312may be configured to render the first switching circuit 324Anon-conductive. The control circuit 312 may be configured to render thethird switching circuit 324C conductive to determine if the second hotdetect circuit 322B is generating the switched-hot detect signalV_(D-SH2). If the second hot detect circuit 322B is generating theswitched-hot detect signal V_(D-SH2) the control circuit 312 may assumethat the hot and switched hot terminals H2, SH2 are wired up backwards,e.g., that the switched-hot terminal SH2 is coupled to the hot side ofthe AC power source 302B. Thus, during normal operation, the controlcircuit 312 may render the first switch circuit 324A conductive beforeattempting to close or open the relay 310B, and non-conductive afterdetecting an edge of hot detect signal V_(D-SH2). In addition and forexample, the control circuit 312 may render the third switching circuit324C conductive at all times during normal operation, such that theswitched-hot detect circuit 322B always generates the switched-hotdetect signal V_(D-SH2). The control circuit 312 may be configured torender the first switching circuit 324A conductive to cause the secondhot detect circuit 320B to begin generating the second hot detect signalV_(D-H2). The control circuit 312 may then monitor the second hot detectsignal V_(D-H2) from the second hot detect circuit 320B, and render thethird switching circuit 324C non-conductive after detecting an edge onthe second hot detect signal V_(D-H2).

What is claimed is:
 1. A load control device for controlling powerdelivered from an AC power source to an electrical device, the loadcontrol device comprising: a first hot detect circuit configured togenerate a first hot-detect signal; a second hot detect circuitconfigured to generate a second hot-detect signal; a first switchingcircuit electrically coupled between the second hot detect circuit and aconnection, the connection adapted to be electrically coupled to earthground or a neutral side of the AC power source; and a control circuitconfigured to receive the first hot-detect signal and the secondhot-detect signal, configured to render the first switching circuitconductive and non-conductive, and configured to determine whether thefirst hot-detect signal and the second hot-detect signal are in phase;wherein, when the control circuit determines that the first hot-detectsignal and the second hot-detect signal are in phase, the controlcircuit is configured to render the first switching circuitnon-conductive; and wherein, when the control circuit determines thatthe first hot-detect signal and the second hot-detect signal are out ofphase, the control circuit is configured to render the first switchingcircuit conductive.
 2. The load control device of claim 1, furthercomprising: a first hot connection and a second hot connection; whereinthe first hot-detect signal indicates a magnitude of a voltage at thefirst hot connection of the load control device and the secondhot-detect signal indicates a magnitude of a voltage at the second hotconnection.
 3. The load control device of claim 1, wherein the first hotdetect circuit is adapted to be electrically connected to a first ACpower source through the first hot connection, and the second hot detectcircuit is adapted to be electrically connected to a second AC powersource through the second hot connection; and wherein the controlcircuit is configured to determine zero-crossing of an AC signalgenerated by the first AC power source based on the first hot-detectsignal and determine zero-crossing of an AC signal generated by thesecond AC power source based on the second hot-detect signal.
 4. Theload control device of claim 3, wherein the first hot connection and thesecond hot connection are adapted to be electrically coupled to amulti-phase AC power source; and wherein the control circuit isconfigured to determine zero-crossing of a first phase of the AC signalbased on the first hot-detect signal and determine zero-crossing of asecond phase of the AC signal based on the second hot-detect signal. 5.The load control device of claim 3, wherein the first phase of the ACsignal and the second phase of the AC signal are out of phase.
 6. Theload control device of claim 1, further comprising: a first switched-hothot detect circuit configured to generate a first switched-hot detectsignal; a second switched-hot hot detect circuit configured to generatea second switched-hot detect signal; a second switching circuitelectrically coupled between the first switched-hot hot detect circuitand the connection; and a third switching circuit electrically coupledbetween the second switched-hot hot detect circuit and the connection; afirst controllably conductive device electrically coupled between thefirst hot detect circuit and the first switched-hot hot detect circuit,the first controllably conductive device configured to control powerdelivered to a first electrical load; and a second controllablyconductive device electrically coupled between the second hot detectcircuit and the second switched-hot hot detect circuit, the secondcontrollably conductive device configured to control power delivered toa second electrical load.
 7. The load control device of claim 6, whereinthe control circuit is further configured to: render the third switchingcircuit conductive; monitor the second switched-hot detect signal whenthe third switching circuit is conductive; and render the thirdswitching circuit non-conductive after detecting an edge on the secondswitched-hot detect signal.
 8. The load control device of claim 6,wherein the control circuit is further configured to: render the secondswitching circuit conductive; monitor the first switched-hot detectsignal when the second switching circuit is conductive; and render thesecond switching circuit non-conductive after detecting an edge on thefirst switched-hot detect signal.
 9. The load control device of claim 6,wherein the control circuit is further configured to send one or moredrive signals to one or more of the first switching circuit, the secondswitching circuit, or the third switching circuit, wherein the one ormore of the first switching circuit, the second switching circuit, orthe third switching circuit, upon receiving the one or more drivesignals, operate independently.
 10. The load control device of claim 6,wherein the control circuit is further configured to send a drive signalto the first switching circuit, the second switching circuit, and thethird switching circuit, wherein the first switching circuit, the secondswitching circuit, and the third switching circuit, upon receiving thedrive signal, operate in coordination with each other.
 11. A loadcontrol device for controlling power delivered from an AC power sourceto an electrical device, the load control device comprising: a first hotdetect circuit configured to generate a first hot-detect signal; asecond hot detect circuit configured to generate a second hot-detectsignal; a first switching circuit electrically coupled between thesecond hot detect circuit and earth ground; and a control circuitconfigured to receive the first hot-detect signal and the secondhot-detect signal, configured to render the first switching circuitconductive and non-conductive, and configured to determine whether thefirst hot-detect signal and the second hot-detect signal are in phase;wherein, when the control circuit determines that the first hot-detectsignal and the second hot-detect signal are in phase, the controlcircuit is configured to render the first switching circuitnon-conductive; and wherein, when the control circuit determines thatthe first hot-detect signal and the second hot-detect signal are out ofphase, the control circuit is configured to render the first switchingcircuit non-conductive until the control circuit receives a user inputto close a relay, and upon receiving the user input to close the relay,the control circuit is configured to render the first switching circuitconductive.